2018-11-15T12:00:08+00:00 ERR (3): Omeka_File_Derivative_Exception: ImageMagick is not properly configured: invalid directory given for the ImageMagick command! in /var/www/vhosts/wokingham-tc.gov.uk/httpdocs/museum/application/libraries/Omeka/File/Derivative/Strategy/ExternalImageMagick.php:82

Yes, it’s looking for the path where ImageMagick is installed so it can make thumbnails of uploaded images.

If it’s installed you should be able to just put the proper path (i.e., /usr/bin or wherever it’s installed on your server) in the Settings form. There’s also a “Test” button there that should tell you if the path is working.